(1) Field of the Invention
The present invention relates to semiconductor devices and methods for fabricating the same, and particularly relates to a structure of a silicide layer and a method for forming the silicide layer.
(2) Description of the Related Art
In general metal oxide semiconductor (MOS) transistors, reduction of parasitic resistance such as contact resistance and wiring resistance is important in increasing operation speed. The reduction of parasitic resistance in such transistors is generally achieved by siliciding upper portions of source/drain regions and upper portions of gate electrodes.
To increase the integration degree of a large-scale semiconductor integrated (LSI) circuit device, reduction of the vertical size as well as the horizontal size is needed. As a technique for reducing the vertical size, the junction depth of a doped layer to be source/drain regions needs to be reduced. However, if the thickness of the doped layer in the semiconductor substrate is small, there arises a problem in which the resistance of the doped layer increases so that the operation speed of the semiconductor device decreases.
To prevent this decrease, it is effective to reduce the source/drain resistance by using a structure in which a metal silicide layer is formed in the surface of the doped layer. As a method for forming the metal silicide layer, a method in which a metal film is deposited over a silicon substrate and a polysilicon film to be a gate electrode, and is then subjected to heat treatment such that silicon and metal react with each other to form silicide in upper portions of source/drain regions and an upper portion of the gate electrode has been conventionally used.
As a material for a silicide layer, a material capable of reducing the amount of silicon consumed during silicidation for a shallow junction is needed. In view of this, a silicide formation technique using, as a material capable of reducing the amount of consumed silicon, nickel (Ni) that forms low-resistance monosilicide has been developed.
However, it is known that NiSi2, which is a disilicide phase of Ni silicide, has a lattice constant fairly close to that of silicon and forms an inverted-pyramidal interface by subsequent high-temperature heat treatment or under inappropriate process conditions. As a method for forming Ni silicide with stability by enhancing resistance (heat resistance) to subsequent high-temperature heat treatment, a method for alloying a silicide has been proposed (see, for example, patent literature 1: U.S. Pat. No. 6,689,688).
In this patent, examples of elements having the effect of stabilizing NiSi, which is a low-resistance monosilicide phase, include Ge, Ti, Re, Ta, N, V, Ir, Cr and Zr (see, for example, non-patent literature 1: Min-Joo Kim et al., “High Thermal Stability of Ni Monosilicide from Ni—Ta Alloy Films on Si(100)”, Electrochem. Solid-State Lett. 6, 2003, G122-G125).
In addition, it is suggested in a report that Hf, which is an element exhibiting physical/chemical properties similar to those of Zr, also has a similar effect (see, for example, non-patent literature 2: R. Xiang (in Tokyo institute of Technology) et al., “Formation of Ni Silicide by Addition of Hf”, Preliminary Material for 65th Annual Meeting of Japanese Society of Applied Physics, P. 708, September 1 to 4, Autumn in 2004 (Lecture No. 2P-M-10)). It is also suggested in other reports that elements such as Mo, Ir, Co and Pt have similar effects (see, for example, non-patent literature 3: Young-Woo Ok, et al., “Effect of a Mo Interlayer on the Electrical and Structural Properties of Nickel Silicides”, J. Electrochem. Soc. 150, 2003, G385-G388, non-patent literature 4: Jer-shen Maa, et al., “Effect of interlayer on thermal stability of nickel silicide”, J. Vac. Sci. Technol. A 19, 2001, pp. 1595-1599, and non-patent literature 5: D. Mangelinck et al., “Enhancement of thermal stability of NiSi films on (100)Si and (111)Si by Pt addition”, Appl. Phys. Lett., 1999, vol. 75, num. 12, pp. 1736-1738).